NHTSA Complaint #11475143 — 2021 TESLA MODEL 3

Car would slow down and suddenly using regenerative braking for no good reason while on Traffic-Aware Cruise Control (part of Autopilot) on very lightly traveled highways, mostly on I-80 in WY, UT, and NV. Incidents happened on 1 to 2% of every mile traveled. I have marked the date as July 3 below, but actually multiple (20 to 50 total) incidents occurred from 7/2 to 7/4, and 7/9 to 7/11. Incidents could occur whether Autosteer was engaged or not. No alarm sounded to indicate that a collision was imminent. If I didn't intervene, the car would sometimes recover almost immediately and slowed only 5 mph, but in other cases it would slow down by 20 mph within 2-3 sec before recovering. Speed limits were typically 75 to 80 mph; I was normally traveling around that speed. Although these highways have low traffic density, my biggest concern is that another car will rear-end mine if it's following too closely. My own observations: 1. The most frequent incident type seemed to occur when there were no vehicles ahead for 15 to 30 sec following distance. Prior to this, Traffic Visualization would sometimes show the next vehicle with uncertainty (flickering in and out or changing size) even though it doesn't normally show a vehicle outside of 4 to 6 sec following distance. Typically that vehicle was a semi-trailer and its appearance to myself (and probably to the cameras) changed due to lighting, details of the trailer, going over a hill, etc. 2. Less frequently, the car would slow down while passing a semi-trailer. Generally Autosteer was not engaged in these cases. 3. High crosswinds could be felt in many cases, but not all. 4. The system seemed much more reliable in areas with more traffic. I'm not sure, but I speculate is that the AI may start looking for vehicles where none exist if it can't easily see any. 5. When mentioned, 2 other Tesla drivers confirmed seeing similar behavior.